Borosilicate glasses



Fatented Aug. 26.1947

uN-lreo enema ,noRosIIJcATE- eLnssEs John E. Stanworth, Sheffield, England, assignor -to GeneralElectric Company. a corporation of .New link No Drawing. Application J annary 9,1947, Serial No. 721,143.. In fireat Britain January "28,

1 This invention relates to glass compositions possessing properties which render them suitable for many uses.

For most purposes, it is desirabl that the glass s-claim -(o1. roe-e54.)

-Thu-s accord-ing to a further I feature of the invention I provide a series of glasses falling within the range above specified and possessing progressively diminishing Coefficients of. thermal compositions provided should be such that they expansion as the percentage of silica and boric can be melted with relative ease. Furthermore, oxide progressively increases and the percenta s it often is necessary for glass compositions to of the remaining constituents progressively depossess good electrical properties, such as high creases, the general characteristic of each of the D. C. electrical resistivity and low A. C. power glasses being maintained substantially uniform. loss. Glasses possessing all these properties have As examples of glass compositions with prohitherto generally included a relatively high pergressively differing thermal expansion charactercentage of lead oxide as one of their constituents. istics within the above mentioned range I may Glasses including lead oxide as a major constitgive the following:

Expansion SiOz B; 3210 Z110 CaFq Na O K20 coellicient Example 55.0 9.0 12.4 7.2 3.2 3.8 as 81.7 Example IL-.- 57.3 13.0 10.4 0.0 2.7 3.2 7.4 74.3 Example III-.- 59.0 10.4 8.4 4.8 2.2 2.0 0.0 01.3 Example 1v--. 01.9 19.8 0.4 3.0 1.7 2.0 4.0 49.7

uent possess, however, certain disadvantages in- All four glasses listed in th above table have asmuch as the lead oxide is readily reduced when excellent electrical properties, e. g. their D. C. the glass is worked in a flame, and if the batch resistivities at 300 C. and 200 C. are respectively is melted in a continuous tank furnace volatiliza- 10 and 10 Example I in the above table will tion of the lead oxide may occur. seal to common soda-lime glass such as one hav- The object of the present invention is to proing the percentage composition by weight viz: vide a range of glasses which, while possessing $102, 2 3, 1 Geo, 6.6; E z most of the advantages associated with lead glass 16.7; are yet free from lead and furthermore possess Each of the abo glasses S s r i y o i s electrical properties which are even superior to neighbour and finally the last glass in the table those of lead glasses hitherto availabl will seal readily to a low expansion borosilicate The present invention comprises glasses falling s, S ch as one having the percentage comwithin the following range of percentage coms t y Weight $102 3, position by weight namely, silica 55-65; boric 0.2; B2 3, N220, oxide 9-25; barium oxide 12.5-4; zinc oxide 7.5-2; The four glasses thus provide a graded seal becalcium fluoride 5-0; sodium oxide and potassium oxide 15-5.

I have found that by varying the constituents of glasses falling within the range above mentioned it is possible to obtain a series of glasses having graded coefficients of thermal expansion. Thus by sealing successively to one another a series of glasses falling within the above mentioned range a thermal expansion characteristic of the composite glass member so produced varies progressively whereby one is enabled to obtain a satisfactory seal between a soda lime and borosilicate glass which is capable of withstanding considerable variation in temperature Without detriment to the seal,

ill

tween soda-lime and borosilicate glass.

Glasses within the above range possess ood melting qualities and good resistance to devitrification.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Glass compositions comprising the heat-reacted product of the following ingredients by weight in the range, of proportions:

Per cent Silica (Si02) H. to Boric oxide (B203) -I 9 to 25 Barium oxide (BaO) 12.5 to 4 Zinc oxide (ZnO) 7.5 to 2 Calcium fluoride (CaFz) 5 to 0 5 Alkali oxide (NelzO-l-KzO) 15 to 3 2. Glass compositions comprising the heat-reacted product of the following ingredients by weight in the proportion specified:

3. Glass compositions comprising the heat-reacted product of the following ingredients by weight in the proportions specified:

Per cent Silica (SiOz) 57.3 Boric oxide (B203) 13.0 Barium oxide (BaO) 10.4 Zinc oxide (ZnO) 6.0 Calcium fluoride (CaFz) 2.7

Sodium oxide (NazO) 3.2 Potassium oxide (K20) 7.4

4 4. Glass compositions comprising the heat-reacted product of the following ingredients by weight in the proportions specified:

Per cent Silica (SiOz) 59.6 Boric oxide (B203) 16.4 Barium oxide (BaO) 8.4 Zinc oxide (ZnO) 4.8 Calcium fluoride (CaFz) 2.2 Sodium oxide (NazO) 2.6 Potassium oxide (K20) 6.0

5. Glass compositions comprising the heat-reacted product of the following ingredients by weight in the proportions specified:

Per cent Silica (SiOz) 61.9 Boric oxide (B203) 19.8 Barium oxide (BaO) 6.4 Zinc oxide (ZnO) 3.6 Calcium fluoride (CaFz) 1.7 Sodium oxide (NazO) 2.0 Potassium oxide (K20) 4.6

JOHN E. STANWORTH. 

